Abstract. Biogenic aerosols play important roles in atmospheric chemistry physics,
the biosphere, climate, and public health. Here, we show that fungi which
actively discharge their spores with liquids into the air, in particular
actively wet spore discharging Ascomycota (AAM) and actively wet spore
discharging Basidiomycota (ABM), are a major source of primary biogenic
aerosol particles and components. We present the first estimates for the
global average emission rates of fungal spores.

Measurement results and budget calculations based on investigations in
Amazonia (Balbina, Brazil, July 2001) indicate that the spores of AAM and
ABM may account for a large proportion of coarse particulate matter in
tropical rainforest regions during the wet season (0.7–2.3 μg m−3). For the particle diameter range of 1–10 μm, the estimated
proportions are ~25% during day-time, ~45% at night, and
~35% on average. For the sugar alcohol mannitol, the budget
calculations indicate that it is suitable for use as a molecular tracer for
actively wet discharged basidiospores (ABS). ABM emissions seem to account
for most of the atmospheric abundance of mannitol (10–68 ng m−3), and
can explain the observed diurnal cycle (higher abundance at night). ABM
emissions of hexose carbohydrates might also account for a significant
proportion of glucose and fructose in air particulate matter (7–49 ng m−3), but the literature-derived ratios are not consistent with the
observed diurnal cycle (lower abundance at night). AAM emissions appear to
account for a large proportion of potassium in air particulate matter over
tropical rainforest regions during the wet season (17–43 ng m−3), and
they can also explain the observed diurnal cycle (higher abundance at
night). The results of our investigations and budget calculations for
tropical rainforest aerosols are consistent with measurements performed at
other locations.

Based on the average abundance of mannitol reported for extratropical
continental boundary layer air (~25 ng m−3), we have also
calculated a value of ~17 Tg yr−1 as a first estimate for the
global average emission rate of ABS over land surfaces, which is consistent
with the typically observed concentrations of ABS (~10³–104 m−3; ~0.1–1 μg m−3).
The global average atmospheric
abundance and emission rate of total fungal spores, including wet and dry
discharged species, are estimated to be higher by a factor of about three,
i.e. 1 μg m−3 and ~50 Tg yr−1. Comparisons with
estimated rates of emission and formation of other major types of organic
aerosol (~47 Tg yr−1 of anthropogenic primary organic aerosol;
12–70 Tg yr−1 of secondary organic aerosol) indicate that emissions
from fungi should be taken into account as a significant global source of
organic aerosol. The effects of fungal spores and related chemical
components might be particularly important in tropical regions, where both
physicochemical processes in the atmosphere and biological activity at the
Earth's surface are particularly intense, and where the abundance of fungal
spores and related chemical compounds are typically higher than in
extratropical regions.